8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets, six torque-transmitting devices, two fixed interconnections and a grounded member. The powertrain includes an engine and torque converter that is selectively connected to one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting devices provide interconnections between various gear members, the input member and the transmission housing, and are operated in combinations of three to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having threeplanetary gear sets that are controlled by six torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission having three planetary gear sets controlled to provideeight forward speed ratios and one reverse speed ratio.

The transmission family of the present invention has three planetarygear sets, each of which includes a first, second and third member,which members may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawing (i.e., left to right, right to left,etc.). Additionally, the first, second or third members of each gear setmay be counted “first” to “third” in any order in the drawing (i.e., topto bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the second memberof the first planetary gear set with the second member of the thirdplanetary gear set.

A second interconnecting member continuously connects the third memberof the first planetary gear set with the second member of the secondplanetary gear set.

The first member of the first planetary gear set is continuouslyconnected to a stationary member (transmission housing/casing). Theoutput member is continuously interconnected with the third member ofthe third planetary gear set.

A first torque-transmitting device, such a brake, selectively connectsthe second member of the first planetary gear set with a stationarymember (transmission housing/casing).

A second torque-transmitting device, such as a clutch, selectivelyconnects the third member of the second planetary gear set with thethird member of the third planetary gear set.

A third torque-transmitting device, such as a clutch, selectivelyconnects the third member of the second planetary gear set with thefirst member of the second planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the second planetary gear set with theinput member.

A fifth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the third planetary gear set with the thirdmember of the second planetary gear set.

A sixth torque-transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with theinput member.

The six torque-transmitting devices are selectively engageable incombinations of three to yield eight forward speed ratios and onereverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes three planetary gear sets20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes a sun gear members 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the sun gear members 32 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear arrangement also includes six torque-transmittingdevices 50, 52, 54, 55, 56 and 57. The torque-transmitting device 50 isa stationary-type torque-transmitting device, commonly termed brake orreaction clutch. The torque-transmitting devices 52, 54, 55, 56 and 57are rotating-type torque-transmitting devices, commonly termed clutches.

The output member 19 is continuously connected with the ring gear member44 of the planetary gear set 40. The sun gear member 22 is continuouslyconnected with the transmission housing 60.

A first interconnecting member 70 continuously connects the planetcarrier assembly member 26 of the planetary gear set 20 with the planetcarrier assembly member 46 of the planetary gear set 40. A secondinterconnecting member 72 continuously connects the ring gear member 24of the planetary gear set 20 with the planet carrier assembly member 36of the planetary gear set 30.

A first torque-transmitting device, such as brake 50, selectivelyconnects the planet carrier assembly member 26 of the planetary gear set20 and planet carrier assembly member 46 of the planetary gear set 40via interconnecting member 70 with the transmission housing 60. A secondtorque-transmitting device, such as clutch 52, selectively connects thering gear member 34 of the planetary gear set 30 with the ring gearmember 44 of the planetary gear set 40. A third torque-transmittingdevice, such as clutch 54, selectively connects the ring gear member 34of the planetary gear set 30 with the sun gear member 32 of theplanetary gear set 30. A fourth torque-transmitting device, such asclutch 55, selectively connects the sun gear member 32 of the planetarygear set 30 with the input member 17. A fifth torque-transmittingdevice, such as clutch 56, selectively connects the sun gear member 42of the planetary gear set 40 with the ring gear member 34 of theplanetary gear set 30. A sixth torque-transmitting device, such asclutch 57, selectively connects the planet carrier assembly member 26 ofthe planetary gear set 20 with the input member 17.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of three to provide eight forward speed ratios and onereverse speed ratio, all with single transition shifts with a doubleoverdrive.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.68, while the step ratio between the reversespeed ratio and first forward ratio is −0.58.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the sun gear member, one for the planetgear carrier member, and one for the ring gear member. The relativelength between the nodes of each lever can be used to represent thering-to-sun ratio of each respective gearset. These lever ratios, inturn, are used to vary the gear ratios of the transmission in order toachieve appropriate ratios and ratio progression. Mechanical couplingsor interconnections between the nodes of the various planetary gear setsare illustrated by thin, horizontal lines and torque transmittingdevices such as clutches and brakes are presented as interleavedfingers. If the device is a brake, one set of the fingers is grounded.Further explanation of the format, purpose and use of lever diagrams canbe found in SAE Paper 810102, authored by Benford, Howard and Leising,Maurice, “The Lever Analogy: A New Tool in Transmission Analysis”, 1981,which is hereby fully incorporated by reference.

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, an output member 19 continuously connected with thefinal drive mechanism 16, a first planetary gear set 20A having threenodes: a first node 22A, a second node 26A and a third node 24A; asecond planetary gear set 30A having three nodes: a first node 32A, asecond node 36A and a third node 34A; and a third planetary gear set 40Ahaving three nodes: a first node 42A, a second node 46A and a third node44A.

The output member 19 is continuously connected with the node 44A. Thenode 22A is continuously connected with the transmission housing 60.

The node 26A is continuously connected with the node 46A viainterconnecting member 70. The node 24A is continuously connected withnode 36A via interconnecting member 72.

A first torque-transmitting device, such as brake 50 engages the nodes26A and 46A via interconnecting member 70 with the transmission housing60. A second torque-transmitting device, such as clutch 52, engages thenode 34A with the node 44A. A third torque-transmitting device, such asclutch 54, engages the node 34A with the node 32A. A fourthtorque-transmitting device, such as clutch 55, engages the node 32A withthe input member 17. A fifth torque-transmitting device, such as clutch56, engages the node 42A with the node 34A. A sixth torque-transmittingdevice, such as clutch 57, engages the nodes 26A and 46A viainterconnecting member 70 with the input member 17.

To establish ratios, three torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row of FIG. 1 b. For example, to establishreverse gear, the brake 50 and clutches 52 and 55 are engaged. The brake50 engages the node 26A with the transmission housing 60. The clutch 52engages the node 34A with the node 44A. The clutch 55 engages the node32A with the input member 17. Likewise, the eight forward ratios areachieved through different combinations of clutch engagement as per FIG.1 b.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members; a first interconnecting member continuouslyconnecting said second member of said first planetary gear set with saidsecond member of said third planetary gear set; a second interconnectingmember continuously connecting said third member of said first planetarygear set with said second member of said second planetary gear set; saidfirst member of said first planetary gear set being continuouslyconnected with a stationary member; six torque-transmitting devices eachfor selectively interconnecting a respective one of said members of saidplanetary gear sets with said input member, with said stationary memberor with another respective one of said members of said planetary gearsets for rotation at a respective common speed, said sixtorque-transmitting devices being engaged in combinations of three toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member; whereinone of said six torque-transmitting mechanisms is selectively engagableto directly connect said third member of said second planetary gear setwith said first member of said second planetary gear set for rotation atthe same speed; wherein another of said six torque-transmitting devicesis selectively engagable to directly connect said second member of saidfirst planetary gear set with said input member for rotation at a speedof the input member; wherein a first of said six torque-transmittingdevices is operable for selectively connecting said second member ofsaid first planetary gear set with said stationary member; wherein asecond of said six torque-transmitting devices is operable forselectively connecting said third member of said second planetary gearset with said third member of said third planetary gear set; whereinsaid one of said torque-transmitting devices is said third of said sixtorque-transmitting devices; wherein a fourth of said sixtorque-transmitting devices is operable for selectively connecting saidfirst member of said second planetary gear set with said input member;and wherein a fifth of said six torque-transmitting devices is operablefor selectively connecting said first member of said third planetarygear set with said third member of said second planetary gear set, saidfifth of said six torque-transmitting devices being engaged in at leasttwo of said at least eight forward speed ratios.
 2. The transmission ofclaim 1, wherein said another of said six torque-transmitting devices isa sixth of said six torque-transmitting devices.
 3. The transmissiondefined in claim 1, wherein said first torque-transmitting devicecomprises a brake, and said second, third, fourth, fifth and sixthtorque-transmitting devices comprise clutches.
 4. The transmission ofclaim 1, wherein said first, second and third members of said first,second and third planetary gear sets comprise a sun gear member, aplanet carrier assembly member and a ring gear member, respectively. 5.The transmission of claim 1, wherein said output member is continuouslyconnected with said third member of said third planetary gear set.
 6. Amulti-speed transmission comprising: an input member; an output member;first, second and third planetary gear sets each having first, secondand third members; said output member being continuously connected withsaid third member of said third planetary gear set; a firstinterconnecting member continuously connecting said second member ofsaid first planetary gear set with said second member of said thirdplanetary gear set; a second interconnecting member continuouslyconnecting said third member of said first planetary gear set with saidsecond member of said second planetary gear set; said first member ofsaid first planetary gear set being continuously connected with astationary member; a first torque-transmitting device selectivelyconnecting said second member of said first planetary gear set with saidstationary member; a second torque-transmitting device selectivelyconnecting said third member of said second planetary gear set with saidthird member of said third planetary gear set for common rotation at onespeed; a third torque-transmitting device selectively directlyconnecting said third member of said second planetary gear set with saidfirst member of said second planetary gear set for rotation at the samespeed; a fourth torque-transmitting device selectively connecting saidfirst member of said second planetary gear set with said input member; afifth torque-transmitting device selectively connecting said firstmember of said third planetary gear set with said third member of saidsecond planetary gear set; a sixth torque-transmitting deviceselectively connecting said second member of said first planetary gearset with said input member for common rotation at a speed of the inputmember; and said six torque-transmitting devices being engaged incombinations of three to establish at least eight forward speed ratiosand at least one reverse speed ratio between said input member and saidoutput member.
 7. The transmission of claim 6, wherein said first,second and third members of said first, second and third planetary gearsets comprise a sun gear member, a planet carrier assembly member and aring gear member, respectively.
 8. A multi-speed transmissioncomprising: an input member; an output member; first, second and thirdplanetary gear sets each having a sun gear member, planet carrierassembly member and ring gear member; said output member beingcontinuously interconnected with said ring gear member of said thirdplanetary gear set; said sun gear member of said first planetary gearset being continuously connected with a stationary member; a firstinterconnecting member continuously connecting said planet carrierassembly member of said first planetary gear set with said planetcarrier assembly member of said third planetary gear set; a secondinterconnecting member continuously connecting said ring gear member ofsaid first planetary gear set with said planet carrier assembly memberof said second planetary gear set; a first torque-transmitting deviceselectively connecting said planet carrier assembly member of said firstplanetary gear set with said stationary member; a secondtorque-transmitting device selectively connecting said ring gear memberof said second planetary gear set with said ring gear member of saidthird planetary gear set; a third torque-transmitting device selectivelydirectly connecting said ring gear member of said second planetary gearset with said sun gear member of said second planetary gear set forrotation at the same speed; a fourth torque-transmitting deviceselectively connecting said sun gear member of said second planetarygear set with said input member; a fifth torque-transmitting deviceselectively connecting said sun gear member of said third planetary gearset with said ring gear member of said second planetary gear set; asixth torque-transmitting device selectively connecting said planetcarrier assembly member of said first planetary gear set with said inputmember; said six torque-transmitting devices being engaged incombinations of three to establish eight forward speed ratios and onereverse speed ratio between said input member and said output member.